Polyolefin films have become a dominant factor in the packaging industry in recent years thanks to a spectrum of favorable properties. However, these materials have several drawbacks that have hampered, to a degree, the realization of their full potential as packaging materials. One such drawback is their lack of good resistance to the transmission of oxygen and moisture vapor.
A very desirable approach to improving the oxygen and moisture vapor transmission of polymer films is the application of a barrier coating, typically a metal coating, to the surface of the film, to thereby form a metallized film. It is to such films that the present invention relates.
TORAY INDUSTRIES, INC. (Japanese Patent Publication No. 61-225049) teaches preparation of metallized polypropylene films by extruding a mixture of polypropylene and a hydrocarbon resin and treating the surface thereof with corona discharge in a nitrogen/CO.sub.2 atmosphere. This treatment inserts amino and/or amido groups into the surface of the film to a depth of about 100 .ANG.. The thus treated film surface is then metallized. To demonstrate the necessity of the nitrogen/CO.sub.2 treatment, Comparative Example 3 of this reference shows poor barrier properties being realized when the corona treatment is carried out in the presence of air rather than in the specified nitrogen/CO.sub.2 atmosphere.
Copending U.S. patent application Ser. No. 08/076,894, filed Jun. 15, 1993, also teaches the preparation of polyolefin films suitable for application of a metal or other type of barrier coating. These films are comprised of a polyolefin, preferably polypropylene, film having a barrier coating receiving layer on one surface thereof. This barrier coating receiving layer is comprised of a polyolefin containing about 1 to 30% by weight of a hydrocarbon resin. The films of the reference application are characterized by excellent adhesion of barrier coatings and excellent barrier properties after application of the barrier coating.
U.S. Pat. No. 4,343,852, issued to Isaka et al., discloses a heat shrink film including a surface layer that optionally can be provided with a metal coating after treatment of the surface layer with a corona discharge. As disclosed, the surface layer for receiving the metal coating can include a variety of different combinations of copolymers, including copolymers of butene-1 and propylene. Such a heat shrink film is not suitable for fabricating extrusion laminated metallized film having good barrier properties, due to the intentionally low dimensional stability towards heat. Moreover, in Examples 2 (column 14) and 3 (column 16), which are the only two examples specifying that the film can be metallized, the film is specified as being corona treated, and the butene-1 content in the propylene/butene-1 copolymers is 20% and 25%, respectively.
U.S. Pat. No. 4,888,237, issued to Balloni et al., discloses a metallized film in which the surface that is provided with a metallized coating is the surface of a crystalline polyolefin layer that is flame treated prior to being metallized. This patent teaches or suggests that the effect of corona treatment or flame treatment in preparing a surface for receiving a metallized coating is not necessarily predictable, and depends, at least in part, on the composition of the surface being treated. Balloni et al. do not suggest or teach any metallized film having a metal coated layer including a butene-1/propylene copolymer within the percentage range of the present invention, and actually, teaches away from such a range; nor do Balloni, et al. suggest or teach that the flame treatment of such a layer would be a desirable treatment of the layer prior to metallization.
U.S. Pat. No. 5,366,796, issued to Murschall, et al., discloses a biaxially oriented multi-layer film that can include a layer having 20% to 80% of a copolymer of propylene and butylene. The patentees teach that the aforementioned layer can optionally be corona or flame treated to enhance the printability of the surface. Although the patentees state that the film is suitable for the production of laminates, including laminates with metallized plastic films, there is no disclosure or suggestion of providing a metal coating on the film as in the present invention. In fact, additives disclosed as being includable in the various layers can adversely effect the bonding of a metal coating to such layers.
U.S. Pat. No. 5,436,041, issued to Murschall et al., discloses a multi-layer film that is sealable on both sides and includes a surface with high surface gloss having good optical properties and good printability. This patent suggests either flame treatment or corona treatment of a layer to be covered with polydialkylsiloxane, but in one preferred form of the invention teaches corona treatment only. Like the Murschall et al. '796 patent, the Murschall et al. '041 patent discloses that the film is suitable for the production of laminates, including laminates with metallized plastic films. However, there is no disclosure or suggestion of providing a metal coating on the film as in the present invention. In fact, additives disclosed as being includable in the various layers can adversely effect the bonding of a metal coating to such layers.
U.S. Pat. No. 4,487,871, issued to Ishibashi, et al., discloses a polyolefin resin composition including a propylenebutene-1 copolymer having a propylene component in a weight percent of at least 70%. This copolymer is present in the range of 96%-80% by weight, and the composition additionally includes 4% to 20% by weight of a high density polyethylene homopolymer or copolymers of ethylene as a main component with other alpha-olefins. The '871 patent discloses only corona treating a surface of the composition to be provided with a metal coating and does not teach or suggest that any enhanced benefits could be obtained by flame treating that surface.
U.S. Pat. No. 5,492,757, issued to Schuhmann et al., discloses a composite film comprised of a base layer, an interlayer and at least one surface layer applied to the interlayer. The base layer can include fillers, including void-creating pigments such as calcium carbonate. The outer surface layer is one or more olefin polymers selected from a long list including polypropylene and copolymers of propylene and butylene. The use of copolymers of propylene and butylene is not exemplified nor is there any teaching of why or how one would apply such copolymers in a composition to enhance metallization. In fact, although the '757 patent suggests laminating the film to other substrates, there is no suggestion of even forming a metallized film of the type forming the subject matter of this invention.
U.S. Pat. No. 4,975,315, issued to Bothe, et al., discloses a metallized film which is corona treated prior to metallizing. There is no suggestion that flame treatment is acceptable, let alone that it would provide superior bond strength between the plastic film and the metal coating. The composition of the metal coating receiving layer is described as including, inter alia, "a propylene/ethylene copolymer having an ethylene content of about 3% by weight or less or of a propylene/ethylene and/or butene-1 copolymer having an ethylene and butene content of about 5% by weight or less in total." (emphasis added). The reference to "a propylene/ethylene and/or butene copolymer having an ethylene and butene content of about 5% by weight or less in total" (emphasis added) is, at best vague, and appears to have been intended to describe a terpolymer of propylene/ethylene/butene-1, as opposed to a propylene/ethylene copolymer and/or a propylene/butene-1 copolymer. Otherwise, the specific reference to the metal coating receiving layer including a propylene/ethylene copolymer having an ethylene content of about 3% would be inconsistent with a subsequent interpretation that the layer could include a propylene ethylene copolymer wherein the ethylene content is of about 5% by weight or less.
U.S. Pat. No. 5,478,643, issued to Peiffer, et al., discloses a matte transfer metallization film for receiving a metal layer, which subsequently is transferred to the final product to be metallized. This patent does not teach a metallized film structure wherein a metal coating is tenaciously and permanently attached as in the present invention.
U.S. Pat. No. 5,489,454, issued to Peiffer, et al., discloses a shrinkable multilayer film having a matte surface, which can be metallized after either corona or flame treatment. The matte surface can include a copolymer of propylene and butylene.
U.S. Pat. No. 5,302,427, issued to Murschall, et al., discloses a multilayer film including a sealing layer having a propylene/butylene copolymer present in a weight percent of 50% of the sealing layer, and wherein the butylene component of the copolymer is 33.2%, by weight of the copolymer. Although the patentees state that the film is suitable for the production of laminates, including laminates with metallized plastic films, there is no disclosure or suggestion of providing a metal coating on the film as in the present invention.
U.S. Pat. No. 4,343,852, issued to Isaka, et al., discloses a heat shrinkable, multilayer product including a surface layer having 50% or more by weight of a propylene/butene-1 copolymer, wherein the butene component is at least 20% of the copolymer.
U.S. Pat. No. 5,326,625, issued to Schuhmann, et al., discloses a sealable, opaque, biaxially oriented film including a core layer containing calcium carbonate, an intermediate layer, and a top layer. The top layer can include a copolymer of propylene and butylene, either alone or in combination with other copolymers or terpolymers, and this top layer can be corona or flame treated, and, if desired, provided with a metal coating.
U.S. Pat. No. 5,277,970, issued to Schuhmann, et al., discloses a sealable, opaque, biaxially oriented white film including a core layer containing calcium carbonate, an intermediate layer, and a top layer that can be surface treated, by means not specifically disclosed, to improve its metallizability.
U.S. Pat. No. 5,281,483, issued to Hwo, discloses metallized films employing a blend of no more than about 10% by weight of low molecular weight, isotactic poly-1-butene and at least about 90% by weight of a propylene polymer. Thus in the Hwo construction the butene is present as a blend with polypropylene, not as a copolymer.